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POCPA3 – DESY, May 21-23, 2012. Elettra digital control PS. Bipolar digital control 30 A – 20 V PS Denis Molaro. Content. [email protected] low current PS requirements Why digital? Resolution & Limit cycles DPWM Resolution H-Bridge Toggle Technique ADC Synchronization

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Elettra digital control ps

POCPA3 – DESY, May 21-23, 2012

Elettra digitalcontrol PS

Bipolar digital control 30 A – 20 V PS

Denis Molaro


Content
Content

  • [email protected] low current PS requirements

  • Why digital?

  • Resolution & Limit cycles

  • DPWM Resolution

  • H-Bridge Toggle Technique

  • ADC Synchronization

  • [email protected] 20 A and 5 A PS

  • INFN Frascati, SPARC PS

  • Conclusion & Consideration

POCPA3 – DESY, 21-23/05/2012



Why digital
Why digital?

  • Easy of PID modification (wide load range for the same current range)

  • Step response optimization for all PS-magnet combination.

  • Galvanic isolation between current sensor and control electronics

POCPA3 – DESY, 21-23/05/2012


Resolution limit cycles
Resolution & Limit Cycles

  • Digital controls are affected by limit cycles

POCPA3 – DESY, 21-23/05/2012


Resolution limit cycles1
Resolution & Limit Cycles

  • Three conditions are required to avoid Limit Cycles[1]

  • Output min step < reading min step

    • (i.e. output resolution > reading resolution)

  • 0 < Integral Gain (Ki) < 1

  • Loop stability (with ADC gain)

Hardware

PID parameters

[1] A.V.Peterchev, S.R. Sanders: Quantization resolution and limit cycling in digitally controlled PWM converters IEEE Transaction on Power Electronics, Volume 18, Issue 1, Part 2, Jan. 2003, pp. 301-308

POCPA3 – DESY, 21-23/05/2012


Resolution limit cycles2
Resolution & Limit Cycles

  • Whenoutput min step > reading min step →

Limit cycles

POCPA3 – DESY, 21-23/05/2012


Resolution limit cycles3
Resolution & Limit Cycles

Whenoutput min step < reading min step →

Stady state stable

POCPA3 – DESY, 21-23/05/2012


Resolution limit cycles4
Resolution & Limit Cycles

  • Output min step (H-Bridge):

  • Reading min step:

  • Example (±5A PS):

  • VDC-Link = 12 V

  • IoutRANGE = 10 A

  • ADC-RES = 16 bit

POCPA3 – DESY, 21-23/05/2012


Resolution limit cycles5
Resolution & Limit Cycles

Limit cycle condition for VDC-Link= 12 V, IoutRANGE = 10 A and ADC-RES = 16 bit

IoutMIN-STEP [µA]

Due to wide range of resistive load a 19 bit of DPWM resolution is required

RLOAD [Ω]

POCPA3 – DESY, 21-23/05/2012


Dpwm resolution
DPWM Resolution

  • Delay-line DPWM has been used (TMS320F2808)

  • Using 4 PWM cycles of dithering

  • 17.8 bit resolution has been achieved

POCPA3 – DESY, 21-23/05/2012


H bridge toggle technique
H-Bridge Toggle Technique

  • A further bit of resolution has been added by a Toggle Technique (Patent Pending) between the two legs of the H-Bridge.

  • For instance with

  • VDC-Link=12, RLOAD=1 and mLSB=1/217.8

POCPA3 – DESY, 21-23/05/2012


H bridge toggle technique1
H-Bridge Toggle Technique

  • A further bit of resolution has been added by a Toggle Technique (Patent Pending) between the two legs of the H-Bridge.

  • Keeping m1 constant, varying m2 (or vice versa)

  • VDC-Link=12, RLOAD=1 and mLSB=1/217.8

POCPA3 – DESY, 21-23/05/2012


H bridge toggle technique2
H-Bridge Toggle Technique

  • Example of Toggle Technique with 2 bit of dithering.

POCPA3 – DESY, 21-23/05/2012


Adc synchronization
ADC Synchronization

  • ∑∆ converter has been used (ADS1252: 24 bit, SPI, SOIC 8 package)

  • Problem: ADC hasn't a start of conversion

∑∆ ADC

ADC

MOD.

CLOCK

SPI

DSP DPWM

SPI

H-Bridge

POCPA3 – DESY, 21-23/05/2012



Infn frascati sparc 30a ps
INFN Frascati - SPARC 30A PS

External 24V 3kW Bulk

Magnet/Load

AC mains

Magnet

Interlock

Ethernet

POCPA3 – DESY, 21-23/05/2012


Infn frascati sparc 30a ps1
INFN Frascati - SPARC 30A PS

POCPA3 – DESY, 21-23/05/2012


Infn frascati sparc 30a ps2
INFN Frascati - SPARC 30A PS

POCPA3 – DESY, 21-23/05/2012


Conclusion consideration
Conclusion & Consideration

  • Digital control is very useful for standardize different range of PS

  • Simplifies the additions of extra features (communication, waveforms...)

BUT

  • Requires digital hardware and software experts for development and modifications

  • Introduces electronic components not easy to repair-replace (FPGA)

SO

  • Could we roll back to the old and simple POWER SUPPLY and not waveform generator with OLED display, please?

POCPA3 – DESY, 21-23/05/2012


That s all folks
That’s all Folks!

Thank You

POCPA3 – DESY, 21-23/05/2012


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